Chemical gettering

Many of the techniques available to purify alkali metals were initially developed to use with liquid sodium as a consequence of its large-scale application in liquid-metal-cooled fast-breeder reactors. These techniques can be summarized as filtration or cold trapping distillation or chemical (gettering). 

Even though a chemical gettering mechanism is proposed in some of these papers, it seems quite likely to us that the decrease of the concentration of these deep levels due to hydrogenation during MBE growth is due to a neutralization by hydrogen of the defects or impurities responsible for these electron traps. 

The sensors are manufactured as differential or absolute pressure sensors. The differential pressure sensors are connected on both sides to absolute pressure sensors, of which the difference between the two pressures is to be measured. They are then evacuated down to a pressure lower than 1 x 10 7 mbar on one side (a chemical getter protects the vacuum of 10 7 mbar from residual degassing). 

Six different types of pump are used to evacuate a vacuum system. The first and most common is the mechanical displacement pump [226,227]. The second is the vapour stream pump [228]. The third is the modem turbomolecular pump [229]. The fourth type is the chemical getter pump. The fifth is the ion pump and the sixth is the cryogenic pump [230]. In technical coating systems, the first three types of pump are preferred. The development of these pumps is narrowly associated with the names W. Gaede, I. Langmuir, C. Burch, K. Hickman and W. Becker [221,225]. Cryogenic pumps have also been used to evacuate technical coating plants. 

External gettering techniques according to Hull (1999) are (i) phosphorus diffusion gettering, (ii) Al gettering, (iii) backside damage and poly-backside seal gettering, (iv) chemical gettering, and... 

Batteries developed for electric vehicles employed evacuated insulation to minimize thickness and weight. Both ABB and SPL used a double-walled, evacuated thermal enclosures with either a fiber board or microporous insulation. Chemical gettering agents were placed within the enclosure to maintain the needed levels of vacuum. This type of system was the only identified design that adequately minimized heat loss while providing the necessary load-bearing capability. 

The largest use for barium is as a getter to remove the last traces of gases from vacuum and television picture tubes. It is ideal for this use because of its combination of high chemical reactivity and low vapor pressure (28—32). In some cases it is used as powder obtained by vaporization ia an electric arc (33). It can also be used as an aluminum ahoy (see Vacuum technology). 

The most important applications of zirconium involve its alloys, Zircaloy. The aUoy offers excellent mechanical and heat-transfer properties and great resistance to corrosion and chemical attack. This, in conjunction with the fact that zirconium has a low neutron absorption cross section, makes this ahoy a suitable choice as a construction material for thermal nuclear reactors and nuclear power plants. Other uses are as an ingredient of explosive mixtures, as getter in vacuum tubes, and in making flash bulb, flash powder (historical), and lamp filaments, in rayon spinnerets, and in surgical appliances. 

Chemical Properties. In the uses of chemical properties the high affinity of the rare earth metals for os gen is primarily involved. This leads to their application as flints, vdierein their highly exothermic reaction with os gen in air is used. On the same properties rests their application as getter metals, vherein residual os gen, as for exanple in amplifier tubes, is bound up. 

The intermetallic compounds were prepared from the best grade of metals commercially obtainable. The rare earth metals, obtained from Research Chemicals, Inc., were 99.9% pure, and cobalt and nickel, obtained from the United Mineral Corp., were 99.999% pure. After each element was weighed to obtain the correct stoichiometric amounts, the compounds were formed by induction melting in a water-cooled copper boat under an argon atmosphere, purified by passage through a titanium-gettering furnace. 

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